Obese people face a much higher risk -- of up to 80 percent -- of dying in a car collision compared with people of normal weight, researchers reported Monday in a specialist journal.

The cause could be that safety in cars is engineered for people of normal weight, not for the obese, they said.

Transport safety scientists Thomas Rice of the University of California at Berkeley and Motao Zhu of the University of West Virginia delved into a US databank on road accidents, the Fatality Analysis Reporting System (FARS).

They dug out data from 1996 to 2008, covering more than 57,000 collisions that involved two cars. This was whittled down to cases in which both parties involved in the collision had been driving vehicles of similar size and types.

The team then compared the risk of fatality against the victim's estimated body mass index (BMI), a benchmark of fat, which is calculated by taking one's weight in kilograms and dividing it by one's height in meters squared.

An adult with a BMI of between 18.5 and 24.9 is considered of normal weight. Below this is considered underweight. Between 25.0 and 29.9 is considered overweight; and 30.0 or above is obese.

The researchers found an increase in risk of 19 percent for underweight drivers compared with counterparts of normal weight.